Electrolytic treatment of metalliferous materials containing metals of the chromium group



July 17, 1923.

- R. E. PEARSON .ET AL ELECTROLYTIC TREATMENT OF METALLIFEROUS MATERIALSCONTAINING METALS OF THE CHROMIUM GROUP Filed June '1. 1922 PatentedJuly 17, 1923.

UNITED STATES RICHARD EDGAR PEARSON, OF LONDON,

PATENT OFFICE.

AND EUSTACE NEVILLE CRAIG, OF HAM COMMON, ENGLAND, ASSIGNORS TO METALPATENTS LIMITED, OF LONDON, ENG- LAND, A BRITISH COMPANY.

ELECTROLYTIC TREATMENT OF METALLIFEROUS MATERIALS CONTAINING METALS OFTHE CHROMIUM GROUP.

Application filed June 1,

To all whom it may concern:

Be it known that we, RICHARD. EDGAR PEARSON, residing at Hanwell,London, England, and EUSTACE NEVILLE CRAIG, residing at Ham Common,Surrey, England, both subjects of the King of England, have inventedcertain new and useful Improvements in the Electrolytic Treatment ofMetalliferous Materials Containing Metals of the Chromium Group, ofwhich the following is a specification.

This invention is for improvements in or relating to the electrolytictreatment of metalliferous materials containing metals of thechromium-group, more particularly for use in the production of metallicpowder, to be employed in the preparation of pressed and sintered barsand the like.

In classifying the metallic elements the term chromium-group is commonlyused to embrace the metals chromium, tungsten, molybdenum and uranium,which have certain properties in common, and where this term occurs inthe present specification and claims, it is to be interpreted in itsordinary sense as signifying the aforesaid metals.

In many ores, waste products or the like, one or other of these metals,either in a free or a combined state, is contained in substantialproportion, but may be much contaminated with other metals orsubstances. One object of this invention is to provide simpleelectrolytic means for concentrating or purifying such ores, wasteproducts or the like.

Broadly stated, the process employed is one in which the anode reactionsin. an electrolytic cell are utilized to oxidize certain materials. 1

According to this invention, a process for concentrating or purifyingmetalliferous material (such, for example, as crude wolframite, crudemolybdenlte, or crude metallic powder) containing a chromiumgroup metalconsists in surrounding an anode with said metalliferous material andwith an electrolyte in which the material is insoluble, but in which theanode products to be isolated are soluble and passing a current from theanode into the electrolyte.

It is to be understood that the electrolyte 1922. Serial No. 565,209.

may be so chosen that the oxide of the chromium-group metal which isformed during electrolysis, is soluble in the electrolyte, whereas theoxides of contaminatmg metals are insoluble. In this case the oxide ofthe chromium'metal comes within the term anode products to be isolated.On the other hand, as more particularly described hereinafter, theelectrolyte may be such that the oxides of contaminating metals aresoluble in the electrolyte, whereas the oxide of the chromium-groupmetal is insoluble. In the latter case it will be appreciated that it isthe oxides of the contaminating metals that are meant when the termanode products to be isolated is used.

When the material to be treated is an ore or the like, it is preferablypowdered and intimately mixed, (for example in the form of a paste) withthe electrolyte.

The metalliferous material may be agitated during the passage ofcurrent.

A suitable apparatus for carrying out one form of the process accordingto the present invention is one in which the metalliferous materialrests upon and is supported by an anode in the form of a plate within anelectrolytic cell.

It is within the scope of this invention to apply the process hereindescribed to the treatment of waste metal (such as scrap molybdenum wireor the like) whereby powdered metallic oxide (for example molybdicoxide) is formed.

The process may also be advantageously applied to the purification ofcrude tungsten or molybdenum powder, as will be more fully describedhereinafter.

Either an acid or an alkaline electrolyte may be employed. In the formercase, when for example an ore is treated, the tungstic or molybdic oxideformed is insoluble in the electrolyte, whereas the oxides of metals(such as iron, manganese, tin, magnesium and the like) which usuallycontaminate the ore are, in general, soluble in the electrolyte. On theother hand, if an alkaline electrolyte be used it is the tungstic ormolybdic oxide which is soluble in the electrolyte and the oxides of thecontaminating metals insoluble. In both cases be dealt with and the usein the process of an acid electrolyte will be considered. Molybdenite isone of the most readily available ores of molybdenum but it contains inaddition to a siliceous gangue, iron, alumina, and the like. Before thismaterial can be utilized for the production of metallic molybdenum, itis desirable to remove the sulphur, and also to eliminate the iron,

alumina and the like. The apparatus which it is preferred to employ isshown in Figure 1 and comprises any desired number of electrolyticcells, each containing an acid electrolyte (for example an aqueoussolution of sulphuric acid). Conveniently each cell is in the form of aninverted bell jar 5 into which the cathode projects from above, whilethe anode is a plate 6 located in the region of the bottom of the cell.The anode may be of any conducting material which is less easilyoxidized than molybdenum and the cathode conveniently comprises apertorated plate 7 of acid-resisting metal. The plate -7 is connected toa central vertical rod 8, which also forms part of the cathode.

The crude molybdenite crushed to a fine powder (for example 200 mesh) ismixed into a paste (like paint) with the electrolyte, and this paste isthen introduced into each cell (which also contains the electrolyte) sothat it rests upon the anode plate therein. Current at a suitablevoltage, say 4-7 volts, is then passed through the cells and oxidationis continued to the desired extent, the paste if required being agitatedfrom time to time in order to keep the surface of the anode plate cleanand to bring fresh portions of the paste into contact therewith. Oneresult of the reaction is that the iron is oxidized and selectivelypasses into solution in the electrolyte. Alumina is similarlyeliminated. The sulphide of molybdenum is converted into oxide which issubstantially insoluble in the electrolyte and therefore remains uponthe anode plate, contaminated only with inert material such as silicangue from which the molybdic oxide may easily separated, say, by ammoniatreatment.

The use of an alkaline electrolyte and the application of the process tothe treatment of wolframite will now be considered;

The apparatus is substantially the same as in the previous example, theelectrolyte in this case, however, being a caustic soda solution (forexample a 25% solution). The anode is preferably not a metal (such asiron) which is oxidized under the conditions of the operation, but ananode of nickel has been successfully used, so also has an anode of analloy of nickel with molybdenum, (12% Mo). As before, the ore is finelypowdered, mixed into a paste with the electrolyte and introduced on tothe anode plate. Current is passed through the cell and oxidation iscarried on to the desired extent, the paste being agitated if requiredduring oxidation.

Wolframite is a tungstate of iron and manganese. i. e., a compound ofoxide of tungsten (W0 with ferrous oxide (Feb) and manganese oxide(MnO), and the ore may contain other metals as well. Asa result of-theanode reaction, the chemical combination of the wolframite is broken up,and the iron and manganese, thus freed, are converted into higher oxides(such as Fe,(), and M11 0 which are insoluble in caustic alkali andremain as a sludge on the anode plate.

Meanwhile the tungstic oxide becomes dissolved in the electrolyte and isobtained in solution as sodium tungstate. In this way it is possible toobtain a product freed from contaminating metals and gangue, andparticularly suitable for use in the production of tungsten ormolybdenum powder, and finally of metallic tungsten or molybdenum.

In the third example of the application of the present invention thestarting material is crude metallic tungsten (or molybdenum) powder. Inthe example under consideration an impure metallic powder was obtainedby reduction of the commercial yellow oxide of tungsten with hydrogen inthe usual way. a a- A suitable iorm of apparatus is illustrated inFigure 2 and comprises any desired number of electrolytic cells 11 eachcontaining a sulphuric acid electrolyte, of specific gravity 1.2. Ineach cell is a porous pot 12 for the anode and a porous pot 13 for thecathode. Into the anode pot the crude tungsten powder mixed withelectrolyte is introduced. The anode to be inserted in the anode pot,consists of a platinum wire 14, and the cathode is a stout rod 15 oflead.

The electrodes are connected to a source of direct current at a voltageof say 5 volts, the current being in the region of 3 amperes. Thecurrent density at the anode is kept as low as possible in order toavoid excessive oxidation of the metallic powder. The process iscontinued to the desired extent, the electrolyte being controlled sothat it remains substantially acid throughout. The result of thereaction is that all those substances which migrate to the cathode, orwhich are oxidized at the anode into compounds soluble in theelectrolyte, are removed from the tungsten powder, thereby effecting asubstantial purification of the latter. The oxy-compounds of sodium,iron and manganese are removed in this way. The soda which passes to thecathode crystallizes out and the major portion of it adheres to thecathode rod with which it may be easily removed from the cell.

Preferably the contents of the anode pot on completion of the anodereaction, are washed and then transferred to the cathode compartment ofan eletrolytic cell again containing a sulphuric acid electrolyte.Treatment at the cathode is carried out under substantially the sameconditions as to concentration of electrolyte, voltage and current asgoverned the anode reaction. Conveniently, the cathode -in this case isa group of nickel-chromium rods, and the anode a rod of lead. The objectof the cathode treatment is to reduce any tungsten which may have becomeoxidized during the anode reaction. Moreover substances which wanderfrom the cathode to the anode (e. g. sulphur and arsenic) are removed bythis treatment. Soluble silica also passes into solution and is thuseliminated. The contents of the cathode pot are washed, dried andsubmitted to a final reduction in hydrogen, after which the powder isready for use in the formation of ressed and sintered bars.

f the impurities to be dealt with in the preparation of metallic powdersuitable for the above use, soda usually presents very considerabledifiiculties and elaborate steps have hitherto been necessary to eflectits removal. It will be seen that the process described above affords aready and efficient means of eliminating soda from the resultantproduct.

The acid (or alkali) used in the electrolyte is chosen to suit theimpurities to be removed, e. g. oxalic acid may be successfully usedwhen sodium is the only predominat ing impurity; hydrochloric acid maybe used if iron is the chief impurity; sulphuric acid is advantageous ifone or more carbides be present; or electrolytes containing these acidsmay be used successively.

We claim:

1. A process for concentrating metalliferous material containing achromiumgroup metal, which process consists in surrounding an anode withsaid metalliferous material and with an electrolyte in which thematerial is insoluble but in which the anode products to be isolated aresoluble, and passing a current from the anode into the electrolyte.

2. A process for concentrating metalliferous material containing achromiumg'roup metal which process consists in preparing an intimatepasty mixture of the metalliferous material in a powdered form with anelectrolyte in which said material is insoluble, but in which the anodeproducts to be isolated are soluble, immersing an anode in said mixture,and passing a current from the anode into the electrolyte.

3. A process for concentrating metalliferous material containing achromiumgroup' metal which process consists in surrounding an anode withsaid metalliferous material and with an acid electrolyte in which thematerial is insoluble but in which the contaminating anode products aresoluble, and passing a current from the anode into the electrolyte.

4. A process for concentrating metalliferous material containing achromiumgroup metal which process consists in surrounding an anode withsaid metalliferous material and with an alkaline electrolyte in whichthe material is insoluble, but in which the anode products of thechromium-group metal are soluble, and passing a current from the anodeinto the electrolyte.

5. A process for concentrating metalliferous material containing achromiumgroup metal, which process consists in surrounding an anode withsaid metalliferous material and with an electrolyte consisting of anaqueous solution of sulphuric acid, and passing a current from the anodeinto the electrolyte.

6. A process for concentrating metalliferous material containing achromiumgroup metal which process consists in surrounding an anode withsaid metalliferous material and with an electrolyte consisting of asolution of caustic soda, and passing a current from the anode into theelectrolyte.

7 A process for concentrating metalliferous material containing achromiumgroup metal which process consists in introducing saidmetalliferous material on to an anode plate within an electrolytic cellcontaining an electrolyte in which the material is insoluble, but inwhich the anode products to be isolated are soluble, and passing acurrent from the anode into the electrolyte.

8. A process for concentrating metalliferous material containing achromiumgroup metal which process consists in introducing into a porousanode chamber within an electrolytic cell, an intimate mixture of saidmetalliferous material and an electrolyte in which it is insoluble, butin which the anode products to be isolated are soluble, immersing ananode in said mixture, and passing a current from the anode into theelectrolyte.

9. A process for concentrating metalliferous material containing achroniumgroup metal which process consists in introducing into a porousanode chamber within an electrolytic cell an intimate mixture of saidmetalliferous material and an electrolyte in which it is insoluble, butin which the anode products to be isolated are soluble, immersing ananode in said mixture, passing a current from the anode into theelectrolyte, and agitating said mixture during the passage of current.

10. A process for concentrating metalliferous material containing achromiumgroup metal in the form of waste metal, which process consistsin surrounding an anode with said metalliferous material and with anelectrolyte in which the material is insoluble, but in which the anodeproducts to be isolated are soluble, and passing a current from theanode into the electrolyte.

11. A process for concentrating metalliferous material containing achromiumgroup metal said material being in the form of crude metallicpowder, which process consists in surrounding an anode with saidmetalliferous material and with an electrolyte in which the material isinsoluble, but in which the contaminating anode products are soluble,and passing a current from the anode into the electrolyte.

12. A process for concentrating metalliferous material containing achromuimroup metal, said material being in the orm of crude metallicpowder, which process consists in surrounding an anode with saidmetalliferous material and with an electrolyte in which the material isinsoluble, but in which the contaminating anode products are soluble,passing a current from the anode into the electrolyte, thereaftersubjecting the powder to the reducing action of the cathode of anelectrolytic cell, and finally washing the reduced product and heatingit in hydrogen in known manner to complete the reduction.

13. A process for purifying crude metallic tungsten powder, whichprocess consists in surrounding an anode with said metalliferousmaterial and with an electrolyte in which the material is insoluble. butin which the contaminating anode products are soluble, and passing acurrent from the anode into the electrolyte.

14. A process for purifying crude metallic tungsten powder whichconsists in preparing an intimate pasty mixture of said powder with anelectrolyte in which it is insoluble, but in which the contaminatinganode products are soluble, immersing an anode in said mixture, andpassing a current from the anode into the electrolyte.

15. A process for purifying crude metallic tungsten powder whichconsists in surrounding an anode with said powder and with anelectrolyte comprising an aqueous solution of sulphuric acid, andpassing a current from the anode into the .electrolyte.

16. A process for purifying crude metallic tungsten powder which processconsists in introducing an intimate mixture of said powder with anelectrolyte in which it is insoluble, but in which the contaminatinganode products are soluble, into a porous pot within an electrolyticcell also containing the electrolyte, immersing an anode in saidmixture, passing a current from the anode into the electrolyte, andagitating the mixture during the passage of the current.

17. A process for the production of tungsten powder for use in themanufacture therefrom of pressed and sintered bars which processconsists in reducing commer cial trioxide of tungsten to an impuremetallic powder by reduction in known manner with hydrogen, introducingsaid impure powder into the anode compartment of an electrolytic cellcontaining an electrolyte in which said powder is insoluble. but inwhich the contaminating anode products are soluble, passing a directcurrent from the said anode into the electrolyte, thereafter subjectingthe powder to the reducing action of an electrolytic cell and finallywashing the reduced product and heating it in hydrogen in known mannerto complete the reduction.

In testimony whereof we have signed our names to this specification inthe presence of two subscribing witnesses.

RICHARD EDGAR PEARSON. EUSTAOE NEVILLE CRAIG. Witnesses:

HARRY S. GREELY, THos. ELBERT.

